Thorium(IV) and Uranium(IV) Thioether and Selenoether Complexes: Synthesis and An–ER₂ (E = S, Se) Bonding Comparison

Reactions of the rigid thioether- and selenoether-containing ligand salts [{Li(AE2Ph2)}2] (E = S or Se; AE2Ph2 = 4,5-bis(phenylchalcogenido)-2,7,9,9-tetramethylacridanide) with ThCl4(dme)2 or UCl4 (for E = Se) afforded the actinide chalcogenoether complexes [(AE2Ph2)2ThCl2] (E = S (1), Se (2)), and [(ASe2Ph2)2UCl2] (3). X-ray crystal structures of 1–3 revealed tetravalent actinide cations complexed to two κ3-coordinated AE2Ph2 ligands, with Th–ER2 and U–ER2 distances below the sum of the covalent radii. Complexes 1–3 provide extremely rare examples of thorium–thioether, thorium–selenoether, and uranium–selenoether bonds, and 1 and 2 contain the shortest known Th–SR2 and Th–SeR2 distances. DFT and QTAIM calculations confirm the presence of significant An(IV)–ER2 interactions in 1–3 and provide insight into the extent of covalency in the An–ER2 bonds.